The present invention relates to novel polymers and their use in antireflective coating compositions in reducing outgassing.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.
The trend towards the minitiarization of semiconductor devices has led to the use of sophisticated multilevel systems to overcome difficulties associated with such minitiarization. The use of highly absorbing antireflective coatings in photolithography is a simpler approach to diminish the problems that result from back reflection of light from highly reflective substrates. Two deleterious effects of back reflectivity are thin film interference and reflective notching. Thin film interference results in changes in critical linewidth dimensions caused by variations in the total light intensity in the resist film as the thickness of the resist changes. Variations of linewidth are proportional to the swing ratio (S) and therefore must be minimized for better linewidth control. Swing ratio is defined by:S=4(R1R2)1/2e−αD where,
R1 is the reflectivity at the resist/air or resist/top coat interface, R2 is the reflectivity at the resist/substrate interface, a is the resist optical absorption coefficient, and D is the resist film thickness.
Antireflective coatings function by absorbing the radiation used for exposing the photoresist, that is, reducing R2, and thereby reducing the swing ratio. Reflective notching becomes severe as the photoresist is patterned over substrates containing topographical features, which scatter light through the photoresist film, leading to linewidth variations, and in the extreme case, forming regions with complete resist loss.
Organic antireflective coatings are usually cured at temperatures above 180° C. Thus, small molecules tend to sublime out of the film during the cure. Outgassing of low molecular weight components is a problem for antireflective coatings in that the components tends to accumulate in bake ovens and in their exhaust plumbing. Sublimed materials can create defects on substrates if dislodged from surfaces on which they accumulated. The current invention uses polymers that are capable of self-crosslinking, which removes the need for low molecular weight crosslinkers.